The main advantage I see of traditional server side rendering (like in Rails/Django) is that you develop a single project, not two (SPA + API).

Instead of api models and client models, you just have models.

Instead of api routes and client routes, you just have routes.

Instead of unit testing api and client, you test one project.

Instead of having the client making N requests to load all the data it needs from the server (and being careful not to return more data than you need for performance reasons), you return an html with all the data it needs in a single request, and nothing more.

In the case of client stacks using SSR (like Next/Nuxt):

Instead of running the SPA on the server so the server returns the html rendered, you just make the server return the html rendered.

The benefit to the developer is higher productivity. The benefit to the end user should follow from that.